The weapons of the stone age Norfolk men who hunted mammoths on what is now the bed of the North Sea, and fragments of the beasts they slaughtered, have turned up in Holland, spotted by an amateur archaeologist in a load of gravel.

The 28 finely worked hand axes are believed to be more than 100,000 years old - possibly far older - and were described yesterday by archaeologist Phil Harding as "the single most important find of ice age material from below the North Sea".

If the dating is correct - and it may be established by the fragments of bone and tooth found in the same load of gravel - the people who worked them by chipping away flakes of stone to leave a blade as sharp as a modern kitchen knife were probably Neanderthal, not Homo sapiens

The lower sea level at the time, with huge volumes of water locked up in the ice age polar ice caps, meant that the area the tools were dredged from, eight miles off Great Yarmouth and under 25 metres of seawater, was then dry land, and Britain was not yet an island.

They were found by an amateur enthusiast, Jan Meulmeester, who regularly hunts through the marine sand and gravel dredged near his home in Flushing, in the south-western Netherlands.

His find was reported last month, and an initial appraisal by Wessex Archaeology, which monitors quarrying and dredging finds, suggested it could be of immense significance. Ancient hand axes have turned up before on the UK's east coast, but their original sites were uncertain, and they dated from a period when archaeologists believed most of the land mass of modern Britain was depopulated.

English Heritage archaeologists are now joining their counterparts in the Netherlands to study the find. What is exciting the experts this time is that the fact that the axes were dredged up with a quantity of silt means they have probably been lying buried in mud exactly where they were dropped so many millennia ago.

Dredging company Hanson has stopped work at the site and a seabed excavation may now be mounted.